The medical community, by using a wide variety of measures, has succeeded in significantly reducing the number of Healthcare-acquired infections (HAI). However, the causative organisms of HAI have become of  significant concern as microorganisms are evolving resistance to the current antimicrobial arsenal.

I would like to discuss in this post, and in following posts a somewhat neglected source of nosocomial pathogens – those pathogens found in the inanimate environment surroundings of the patients, and how they can contribute to HAI. In this first post I will briefly discuss what pathogenic bacteria have been found in the clinical environment.

Several important bacterial pathogens, including hard to treat bacteria such as Methicillin resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococci (VRE), Clostridium difficile  Acinetobacter baumannii, and Pseudomonas aeruginosa can be  found on different surfaces in the hospital environment (1, 2).

Most of these bacteria originate mainly from infected and/or colonized patients that shed them into the hospital environment. However, contamination can be found in rooms of  uninfected or non-colonized patients.  The contamination of uninfected or non colonized patient rooms has been reported for C. difficile, MRSA and VRE.

C. diff
C. diff

C. difficile was identified on 16-17% of samples from the rooms of patients without known C. difficile infection (3, 4).


S. aureus

MRSA was cultured from 43% of beds used by patients not known to be MRSA positive (5).



VRE was cultured from 13% of surfaces in the rooms of patients with unknown VRE status (6).

Contamination of rooms of unaffected patients is most likely to be due to continued viability of organisms shed by previous occupants and may be also shed from visitors or asymptomatic carriers (7).

One controversy is the wide variation in the reported frequency of environmental contamination. There are numerous explanations for the variety including the degree of shedding by the patient, the sampling methodology, the cleaning of the particular environment and whether there is an ongoing outbreak at the time of sampling.

Methodological differences in sample collection and culture make comparisons between studies difficult and in some cases the true level of environmental contamination may be underestimated.

We would like to hear your feedback or thoughts on bacterial environmental contamination, and look for my next post where we will be looking at what fungi can be found in the environment!

References quoted

  1. Sexton et al. Environmental reservoirs of methicillin-resistant Staphylococcus aureus in isolation rooms: correlation with patient isolates and implications for hospital hygiene. J Hosp Infect 2006;62:187-194.
  2. Eckstein et al. Reduction of Clostridium difficile and vancomycin-resistant Enterococcus contamination of environmental surfaces after an intervention to improve cleaning methods. BMC Infect Dis 2007;7:61
  3. Dubberke et al. Prevalence of Clostridium difficile environmental contamination and strain variability in multiple health care facilities. Am J Infect Cont 2007;35:315-318
  4. Dumford et al. What is on that keyboard? Detecting hidden environmental reservoirs of Clostridium difficile during an outbreak associated with North American pulsed-field gel electrophoresis type 1 strains. Am J Infect Control 2009;37:15-19
  5. French GL, Otter JA, Shannon KP, Adams NM, Watling D, Parks MJ. Tackling contamination of the hospital environment by methicillin-resistant Staphylococcus aureus (MRSA): a comparison between conventional terminal cleaning and hydrogen peroxide vapour decontamination. J Hosp Infect 2004;57:31-37
  6. Trick et al. Patient colonization and environmental contamination by vancomycin-resistant enterococci in a rehabilitation facility. Arch Phys Med Rehab 2002;83:899-902
  7. Riggs et al. Asymptomatic carriers are a potential source for transmission of epidemic and nonepidemic Clostridium difficile strains among long-term care facility residents. Clin Infect Dis 2007;45:992-998

Images courtesy of Center for Disease Control and Prevention-available here